{"id":"CVE-2026-98158","revision":"699c8b0f567c4fcfbad7d2319e08e18b","records":[{"revision":"699c8b0f567c4fcfbad7d2319e08e18b","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-98158","aliases":[],"title":"ppp_async: drop the errored frame instead of resetting its headroom","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nppp_async: drop the errored frame instead of resetting its headroom\n\nppp_receive_nonmp_frame() prepends a two-byte direction tag before running\nthe pass/active BPF filters:\n\n\t*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);\n\nNothing on the receive path guarantees those two bytes of headroom. The\nframe-error path in ppp_async's process_input_packet() resets a reused skb's\nheadroom to zero while claiming to restore it to a freshly allocated state -\nbut a fresh skb from dev_alloc_skb() carries NET_SKB_PAD:\n\n\terr:\n\t\tif (skb) {\n\t\t\t/* make skb appear as freshly allocated */\n\t\t\tskb_trim(skb, 0);\n\t\t\tskb_reserve(skb, - skb_headroom(skb));\n\t\t}\n\nap->rpkt still points at that skb, so the next frame is reassembled into it\nwith no headroom at all. A peer that sends a bad-FCS frame followed by one\nbeginning ff 03 then leaves a single byte of headroom by the time the filter\ntag is pushed, which lands one byte below skb->head:\n\n skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000\n data:ffff888003c0ffff tail:0x30 end:0x640 dev:\n kernel BUG at net/core/skbuff.c:214!\n RIP: 0010:skb_panic+0x13e/0x230\n Call Trace:\n skb_push+0xbd/0x100\n ppp_receive_nonmp_frame+0x48a/0x1d10\n ppp_input+0x4e9/0x2f80\n ppp_async_process+0x2a/0xe0\n tasklet_action_common+0x20f/0x8a0\n handle_softirqs+0x18e/0x590\n Kernel panic - not syncing: Fatal exception in interrupt\n\nZeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb()\ngives the rest of the receive path. Besides the filter panic above, when CCP\ncompression is enabled ppp_decompress_frame() hands skb->data - 2 to\n->decompress()/->incomp(), which then reads out of bounds before skb->head\nfor the same reason.\n\nRather than restore the headroom, drop the errored frame - as ppp_synctty\nalready does on its error path - and clear ap->rpkt so the next frame is\nreassembled into a fresh skb with proper headroom. This is simpler and fixes\nboth the filter under-panic and the CCP out-of-bounds read.\n\nThe original V1 of this patch made room in ppp_receive_nonmp_frame() with\nskb_cow_head(); Eric pointed out that fixing the root cause in the transport\nis the right approach.\n\nFound by fuzzing the PPP receive path with a mutating peer on a pty; it is an\ninteresting (remote) DoS: root configures PPP, the peer supplies two crashing\nframes. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a\nsecond, and returns cleanly with this applied.","state":0,"publishedAt":"2026-09-25T10:36:27.608+00:00","modifiedAt":"2026-10-19T09:14:52.068+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"drivers/net/ppp/ppp_async.c\"\n ],\n \"versions\": [\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"25f354c55b8435d1f51b8a0a05a3cfe429358523\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"a86a17745c3e1c6fadd4d6e90c03552dfe531c8c\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"ff035780adb0f49dc2c7ada26b4697849a68bec8\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"c4bb894362d224b699e2f95c6c26707d9654e4a3\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"0c53eb14975f029abd6b26896a460f0d2aaefe6b\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"717137221c7d90e7c98bda9a370c9da6cbf015e5\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"6722e78c90054101e6797d5944cdc81af9897a0a\",\n \"lessThan\": \"8dc5d98a16fa23c00999aecf10018c9f69fa5bf4\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"drivers/net/ppp/ppp_async.c\"\n ],\n \"versions\": [\n {\n \"version\": \"2.6.15\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"2.6.15\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.10.271\",\n \"lessThanOrEqual\": \"5.10.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"5.15.222\",\n \"lessThanOrEqual\": \"5.15.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.1.189\",\n \"lessThanOrEqual\": \"6.1.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.6.158\",\n \"lessThanOrEqual\": \"6.6.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.12.111\",\n \"lessThanOrEqual\": \"6.12.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.18.53\",\n \"lessThanOrEqual\": \"6.18.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.2.7\",\n \"lessThanOrEqual\": \"7.2.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"7.3\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523","https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8","https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3","https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b","https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5","https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98158","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-98158","identifiers":["CVE-2026-98158"]},"retained":false,"historicalAffected":[]}],"coverage":[]}